Cejas Cooling & Construction

Between Oil and Machine

Refrigerants and the Machines That Breathe Them

Types of Refrigerants and Their Characteristics

Refrigerants are working fluids. They’re the lifeblood of the refrigeration cycle—changing state to move heat. Common refrigerants include:

  • R-410A: A near-azeotropic blend of R-32 and R-125. High pressure. Requires POE oil. GWP ~2,088.
  • R-22: Legacy refrigerant. Phased out due to ozone depletion. Lower pressure. Uses mineral oil.
  • R-134a: Used in medium-temperature refrigeration and automotive AC. GWP ~1,430. Pure compound.
  • R-32: A component of R-410A. Now used on its own in many new systems. Higher pressure. GWP ~675.
  • R-454B: Low-GWP blend replacing R-410A. Slightly flammable (A2L). GWP ~466.

Physical Properties

  • Boiling Point: A key to heat transfer. R-410A: -55.3°F. R-22: -41°F. R-134a: -15.3°F.
  • Molecular Weight: Affects pressure and mass flow rate. R-410A: ~72.6. R-134a: ~102.
  • Pressure-Temperature Relationship: Higher pressure = higher boiling point. Refrigerants must match the system’s pressure design.

Saturation Temperature

The temperature at which a refrigerant boils (or condenses) at a given pressure. It’s not fixed—it depends on the system’s operating pressure.

Example:

  • At 118 PSIG, R-410A has a saturation temp of ~40°F.

Pressure Enthalpy Diagram

This graph visualizes the entire refrigeration cycle:

  • Evaporation (low pressure, heat absorption)
  • Compression (rising pressure and enthalpy)
  • Condensation (high pressure, heat rejection)
  • Expansion (enthalpy drop through metering device)

Superheat and subcooling are visible zones on this chart.

Superheat and Subcooling

  • Superheat: Temp of vapor above its boiling point. Ensures no liquid hits the compressor.
  • Subcooling: Temp of liquid below its condensing point. Ensures only liquid enters the metering device.

Evaporator

  • Function: Absorbs heat from indoor air as refrigerant boils.
  • High superheat = underfeeding or low charge
  • Low superheat = floodback or TXV issue

Compressor

  • Function: Increases pressure and temperature. Moves vapor through the cycle.
  • Types: Scroll, rotary, reciprocating

Condenser

  • Function: Rejects heat outdoors. Refrigerant changes from vapor to liquid.
  • High subcooling = overcharge or restricted metering device
  • Low subcooling = undercharge or poor heat transfer

Metering Devices

  • Capillary Tubes: Fixed orifice. Cheap, reliable, but sensitive.
  • TXV (Thermostatic Expansion Valve): Maintains constant superheat.
  • EEV (Electronic Expansion Valve): Precise control. Used in advanced systems.

Choosing a Refrigerant

Look at:

  • Pressure compatibility
  • Lubricant requirements
  • Toxicity and flammability (ASHRAE Safety Groups: A1 = safe, A2L = mildly flammable)
  • Environmental impact (ODP and GWP)

Storage and Handling

  • Always use recovery cylinders with matching labeling.
  • Use a recovery machine to extract refrigerant.
  • Store cylinders upright in a cool, ventilated area.

Summary

Refrigerants aren’t just chemicals—they’re physics in a bottle. Understanding their properties, behaviors, and handling methods is what separates a technician from a true HVAC craftsman. Master this, and you speak the secret language of pressure and heat.

Next: electricity and magnetism—the invisible forces powering every system you touch.